1. Field of the Invention
The present invention relates to a conveyance device that conveys a thin substrate such as glass.
2. Description of the Related Art
Production of flat panel displays as typified by liquid crystal displays frequently uses a conveyance device for levitating and conveying a thin substrate such as thin glass in order to conveying the substrate without scratching it. Such a conveyance device is usually comprised of a levitation device that emits compressed air and further a belt conveyor or a roller conveyor that comes in contact with the levitated substrate and gives it a driving force.
Dusts adhering to the substrate or scratches thereon considerably affect the quality of the displays. One of causes for dust adhesion or making scratches on the surface is that the glass substrate gets in contact with the conveyance device or such. On the other hand, as the glass substrate is 0.7 mm or less in thickness and is therefore flexible, it is emphasized to convey the substrate with keeping its flatness for the purpose of preventing collision in the course of conveyance. There is a growing need for use of thinner glass in these days and thus conveyance thereof with keeping its flatness becomes more and more difficult.
Japanese Patent Applications Laid-open No. 2008-066661 and 2008-260591 disclose related arts. The former discloses an art of a conveyance device comprising a belt conveyor. According to this art, the belt is comprised of projections arranged at even intervals and the projections come in contact with a glass substrate to convey it.
The latter discloses an art of a conveyance device comprising a roller conveyor. According to the art of the PTL 2, an event where deformation of a glass substrate in which a pass line central portion of the glass substrate considerably floats upward or falls downward becomes prominent. To solve this problem, the air feeding rate from an air table unit at the lateral central position is regulated to suppress deformation of the glass substrate.